We explain what an animal cell is and the theories of its possible origin. In addition, its parts and the differences with the plant cell.
What is an animal cell?
An animal cell is a type of eukaryotic cell (that is, endowed with a true nucleus) present in various tissues of the living beings belonging to kingdom Animalia. These cells are adapted to the biochemical functions of the animal organism, such as its metabolism and forms of nutrition (heterotrophic).
Since animals are all complex multicellular beings, their cells have a very high level of specialization, that is, depending on the tissue to which they belong, they fulfill specific functions that define their morphology, their function and their needs. A human beingFor example, it has about 44 different cell types.
The emergence of the animal kingdom, unlike the vegetable, starts from a question: it is not known science certain how the transit between protozoa and metazoans, that is, between unicellular life and specialized multicellular organization, since there is no evidence of this in the fossil record. There are three theories in this regard:
- Colonial origin. This theory states that complex animal life would have arisen from colonies of cells that lived together and that, by adapting to survival needs, increasingly specialized in some defensive or logistical aspect essential for the colony: movement, defense, organization, etc.
- Symbiotic origin. This theory assumes that multicellular life would come from a complex case of symbiosis, in which many cells began to cohabit in a positive way for all, helping and caring for each other to such a degree that little by little they needed more and more until they began to operate as a single individual.
- Origin by cellularization. Part of the idea that multicellular animals would be the consequence of the cellularization processes of the cell nuclei of a primitive organism, whose cells had more than one nucleus. Thus, by generating compartments to protect them, it would have been forming cells within the cell and growing at an internal level of complexity.
Parts of an animal cell
The usual parts of an animal cell are:
- Core. Like all eukaryotes, animals have cells with a well-defined nucleus in which all their genetic material is housed (DNA) organized in chromosomes and fulfilling key roles in the cell reproduction. The nucleus is made up of an aqueous suspension called nucleoplasm, in which DNA and other nuclear structures are immersed, and which is wrapped in a nuclear membrane that allows exchange with the cytoplasm.
- Plasma membrane. It is the selective lipoprotein membrane that covers the cell and distinguishes its interior from its exterior, allowing the entry of desired substances and the exit of metabolic waste.
- Cytoplasm. It is the interior of the cell, where the nucleus and cell organelles are found. It is a very fine, granular colloidal substance, where many metabolic processes take place.
- Mitochondria. They are the energy plants of the cell, responsible for the synthesis of ATP (molecule from chemical energy) from cellular nutrients (a process known as "cellular respiration").
- Lysosomes. They degrade the material that enters the cell (heterophagy) or produced within it (autophagy), that is, they are in charge of cellular digestion and are created by the golgi apparatus.
- Golgi apparatus. Common in animal and plant cells, it is a series of membranes within the cell, which serve as a transport channel for protein and other substances through a system of vesicles into and out of the cytoplasm.
- Endoplasmic reticulum. It is a series of interconnected flattened tubules and sacs, made up of fatty acids. It is divided into two domains with different functions: the rough endoplasmic reticulum, covered with ribosomes in which protein synthesis occurs; and the smooth endoplasmic reticulum, vital in the synthesis of lipids, in cell detoxification, as well as in the absorption and release of calcium from the cell.
- Centriole. It is a cylindrical organelle made up of three triplets of microtubules, part of the cytoskeleton (cell framework), and located in the cytoplasm, in a region called diplosome. These ducts have an important role in the transport of organelles in the cell and also in the processes of mitosis or cell division.
- Chromatin This is the name given to the set of DNA, histone and non-histone proteins that are found in the cell nucleus and that make up the genetic material of the cell. Its basic units of information are nucleosomes.
Differences between animal cell and plant cell
Plant and fungal cells have a rigid cell wall.
The differences between the animal and plant cells can be summarized as:
- Cellular wall. Cells plants and of mushrooms They have a rigid cell wall, which limits their growth but makes them more compact. This wall is located outside the plasma membrane and is made up of cellulose (in the case of plants) or chitin (in the case of fungi). In animal cells it is not present.
- Size. Animal cells are smaller than plant cells, perhaps because they do not have a central fluid-filled vacuole, but rather small and numerous vesicles in their cytoplasm.
- Chloroplasts Since plants do photosynthesis, their cells have chloroplasts: organelles in which chlorophyll is housed, essential for obtaining energy from the sunlight. Animal cells therefore lack such organelles and instead have what is necessary for glucose oxidation (respiration).